Prior work has been done in making machines that assemble structures from discrete parts. Hiller et al. showed a method of parallel part placement of voxel spheres in [J. Hiller and H. Lipson, “Methods of Parallel Voxel Manipulation for 3D Digital Printing,” in Proceedings of the 18th solid freeform fabrication symposium, 2007, p. 12]. These voxels, however, do not interlock in a structural way and so a binder must be used after depositing the spheres. Assembly machines have also been created for use in assembling micro-electronics. [see E. D. Kunt, A. T. Naskali, and A. Sabanovic, “Miniaturized modular manipulator design for high precision assembly and manipulation tasks,” 2012 12th IEEE Int. Work. Adv. Motion Control, pp. 1-6, March 2012]. These machines operate as pick-and-place machines, having an external magazine of parts from which parts are picked but do not physically register the toolhead to the structure or circuit board. Active research in assembling structures with robotic arms looks to incorporate force sensing to do closed loop force control rather than displacement control. [see A. Stolt, M. Linderoth, A. Robertsson, and R. Johansson, “Force controlled assembly of emergency stop button,” 2011 IEEE Int. Conf. Robot. Autom., pp. 3751-3756, May 2011].
This invention describes a set of machines capable of building structures by the additive assembly of discrete parts. These digital material assemblies (described, in part, in U.S. Pat. No. 7,848,838) constrain the constituent parts to a discrete set of possible positions and orientations. In doing so, the structures exhibit many of the properties inherent in digital communication such as error correction and fault tolerance and allow the assembly of precise structures with comparatively imprecise tools. The machines responsible for assembling digital materials should leverage, to the extent possible, the interlocking and error-correction naturally present in the discrete parts.
Interest in additive manufacturing has recently been spurred by the promise of multi-material printing and the ability to embed functionality and intelligence into objects. The present invention discloses an alternative to additive manufacturing, introducing an end-to-end workflow in which discrete building blocks are reversibly joined to produce assemblies called digital materials. The present invention describes the design of the bulk-material building blocks and the devices that are assembled from them. The present invention details the design and implementation of an automated assembler, which takes advantage of the digital material structure to avoid positioning errors within a large tolerance. To generate assembly sequences, a novel CAD/CAM workflow is used for designing, simulating, and assembling digital materials. The structures assembled using this process have been evaluated, showing that the joints perform well under varying conditions and that the assembled structures are functionally precise. A very similar evaluation method applied to more standardized material samples has been described [see Luo, Xiangcheng, Chung, D. D. L., Material contacts under cyclic compression, studied in real time by electrical resistance measurement, Journal of Materials Science, 35 (2000) 4795-4801]. However, the present invention details an evaluation method for digital materials.
There has been recent interest in fabrication processes and material systems that enable functionality to be embedded within structure. Researchers in the fields of additive manufacturing and digital materials, in particular, have been exploring ways of accomplishing this.
Multi-Material Additive Manufacturing
The recent interest in additive manufacturing has, in part, been spurred by the promise that complex multi-material structures can be printed with embedded functionality. Recent work has demonstrated that 3D printing enables the fabrication of ultralight lattices [see B. G. Compton and J. a. Lewis, “3D-Printing of Lightweight Cellular Composites,” Adv. Mater., p. n/a-n/a, June 2014], auxetic energy-damping structures [see S. Shan, S. H. Kang, J. R. Raney, P. Wang, L. Fang, F. Candido, J. a. Lewis, and K. Bertoldi, “Multistable Architected Materials for Trapping Elastic Strain Energy,” Adv. Mater., p. n/a-n/a, June 2015], and self-folding chains [see D. Raviv, W. Zhao, C. McKnelly, A. Papadopoulou, A. Kadambi, B. Shi, S. Hirsch, D. Dikovsky, M. Zyracki, C. Olguin, R. Raskar, and S. Tibbits, “Active Printed Materials for Complex Self-Evolving Deformations,” Sci. Rep., vol. 4, p. 7422, 2014]. Commercial 3D printers are able to print objects from a wide range of materials including sintered metals and nylon, UV-cured resin, and thermoplastics like ABS and PLA. However, these printers are generally restricted to printing a single material at a time and only a small number of commercially available printers are able to simultaneously print with multiple materials; those that can, are limited to printing plastics with a relatively narrow range of material properties.
None of these printers, however, have been able match the properties and variety of electronic materials needed to print a full range of electronic devices. While researchers have recently developed conductive ink formulations that enable the controlled deposition of highly-conductive traces [see A. Russo, B. Y. Ahn, J. J. Adams, E. B. Duoss, J. T. Bernhard, and J. A. Lewis, “Pen-on-Paper Flexible Electronics,” Adv. Mater., vol. 23, no. 30, pp. 3426-3430, 2011; D. Zhao, T. Liu, J. G. Park, M. Zhang, J. M. Chen, and B. Wang, “Conductivity enhancement of aerosol jet printed electronics by using silver nanoparticles ink with carbon nanotubes,” Microelectron. Eng., vol. 96, pp. 71-75, 2012], they have not yet been commercialized (although two are very close to market [see “Voltera.” [Online]. Available: http://voltera.io/. [Accessed: 26 Nov. 2015]; “Voxel8.” [Online]. Available: http://www.voxel8.co/. [Accessed: 27 Nov. 2015]]). Still, these formulations are one to two orders of magnitude less conductive than bulk metal and often require a post-bake processing step to evaporate the solvent, which limits the substrate material choice.
With these conductive inks, researchers have started to show that it is possible to print functional electronics. Using specially formulated anode and cathode inks, researchers are able to print lithium ion [see K. Sun, T. S. Wei, B. Y. Ahn, J. Y. Seo, S. J. Dillon, and J. a. Lewis, “3D printing of interdigitated Li-ion microbattery architectures,” Adv. Mater., vol. 25, no. 33, pp. 4539-4543, 2013] and zinc-air [see E. Malone, K. Rasa, D. Cohen, T. Isaacson, H. Lashley, and H. Lipson, “Freeform fabrication of zinc-air batteries and electromechanical assemblies,” Rapid Prototyp. J., vol. 10, no. 1, pp. 58-69, 2004] batteries. In another study, the conductive inks were conformally printed on 3D substrates to fabricate efficient antennas [see J. J. Adams, E. B. Duoss, T. F. Malkowski, M. J. Motala, B. Y. Ahn, R. G. Nuzzo, J. T. Bernhard, and J. a Lewis, “Conformal printing of electrically small antennas on three-dimensional surfaces,” Adv. Mater., vol. 23, no. 11, pp. 1335-40, March 2011]. Ink-jet printing has also been used in similar ways to deposit highly conductive silver traces to create electromechanical functionalities like an electrostatic motor [see S. B. Fuller, E. J. Wilhelm, and J. M. Jacobson, “Ink-jet printed nanoparticle microelectromechanical systems,” J. Microelectromechanical Syst., vol. 11, no. 1, pp. 54-60, 2002]. While 3D printers are capable of fabricating objects from a wide range of materials, they all fundamentally perform more-or-less the same task of carefully positioning a print head and depositing or fusing a precise amount of material. If the speed of the positioning is not precisely mapped to the rate of deposition or fusing of material, the fabricated object will have bumps or voids. The accuracy of the final product is therefore ultimately determined by the accuracy of the machine. A model printed on a hobbyist's home 3D printer will come out markedly different from the same model printed on a million dollar commercial 3D printer.